1. Field of the Invention
The present invention relates to a microwave plasma treating method and a system therefor and, more particularly, to a method of and a system for microwave plasma treatment, which are suitable for etching or forming a film on a specimen such as a semiconductor element substrate with plasma.
2. Description of the Prior Art
A microwave plasma treating system of the prior art provides a uniform plasma density, as disclosed in Japanese Patent Laid-Open No. 16732/1990 (corresponding to U.S. Pat. No. 4,877,509), for example, by disposing circularly polarized wave transforming means in a waveguide, in which the microwaves propagate, to rotate the oscillating direction of the microwaves by 90 degrees for every quarter period so that the oscillating direction may make one rotation for one period.
This prior art system has not taken into consideration the phase velocity of the microwaves, which will exert influences upon the efficiency for energy transformations from the microwaves to the charged particles in the plasma, so that the density of plasma is yet to be increased.
In another prior art system (as disclosed in Japanese Patent Laid-Open No. 187919/1989), on the other hand, a cylindrical dielectric member is fitted in the circumferential wall of a plasma generating chamber to provide a uniform electric field in the plasma generating chamber so a film can be uniformly formed on the surface of a specimen while blocking formation of the plasma at the outer circumference of the plasma generating chamber, to enhance the energy efficiency.
This prior art system also has failed to take into consideration into the phase velocity of the microwaves, which will exert influences upon the efficiency for energy transformations from the microwaves to the charged particles in the plasma, so that the density of the plasma fall short of a desired level.
Another prior art system relating to the present invention is disclosed in Japanese Patent Laid-Open No. 82524/1990 (corresponding to U.S. Pat. No. 4,960,073). According to this disclosure, a frusto-conical block is disposed in the plasma generating chamber to introduce the microwaves efficiently without any loss and uniformly into the plasma generating chamber so that the plasma may be generated uniformly at high density all over the inside of the plasma generating chamber. This prior art system also has failed to take into consideration the phase velocity of the microwaves, which will exert influences upon the efficiency for the energy transformations from the microwaves to the charged particles in the plasma.